In such an arrangement, the dashboard, which is situated inside the vehicle and below the windscreen, comprises a dashboard body that has a back face carrying an airbag module, which module comprises an enclosure containing the airbag and inflation means for inflating said airbag, and facing the corresponding opening in the dashboard body.
The opening, which is generally rectangular, is closed by one or two flaps, each of which has an edge that is hinged to a corresponding transverse edge of said opening. A firing channel, forming a spacer, is interposed between the airbag module and the back face of the dashboard body.
The front face of each flap and the front face of the dashboard body constitute a substantially continuous convex surface. Said convex surface may be covered by a skin, in order to make the flap substantially invisible to an occupant of the vehicle.
When an impact is detected, the airbag inflates automatically, so that it exerts pressure on the inside face of the flap, thereby causing it to open, against the covering that tears. That enables the airbag to be deployed through the dashboard towards the inside of the vehicle, in such a manner as to be interposed between an occupant of the vehicle and the dashboard.
The flap opens and the airbag is fully inflated within a lapse of time that must be sufficiently short to protect the occupant of the vehicle by preventing the occupant's head from hitting the dashboard or the windscreen under the effect of the impact.
The airbag inflating thus causes the flap to open, also very rapidly, so that the free edge of said flap is actually stopped by the windscreen that it generally hits, thereby causing the opening movement of the flap to cease.
In practice, it can happen that the impact of the flap against the windscreen breaks the windscreen, and naturally that is undesirable in view of the fragments of glass that could injure the occupant of the vehicle, and in view of the repair cost that is increased by the need to replace the windscreen.
In order to avoid destroying the windscreen, consideration has been given to closing the opening in the dashboard body by means of two rectangular flaps, one opening upwards and the other downwards. The flap opening upwards is then of smaller size so that its opening movement is stopped by the dashboard itself, rather than by the windscreen.
Unfortunately, implementing two rectangular flaps constitutes a solution that is complex in terms of production, which increases the overall cost.
Alternatively, the opening is closed by a single flap made of a material that is sufficiently flexible to reduce the risk of the windscreen breaking, but that solution remains difficult to implement. It is necessary to reconcile two contradictory requirements: the flap must be sufficiently flexible not to break the windscreen, but it must also be stiff enough not to deform when it is closed, so that the dashboard continues to have its original curve.
In addition, since the flap continues to be stopped by the windscreen, even if said flap is flexible, the opening energy continues to be fully transferred to the windscreen, so that it cannot be totally guaranteed that it will not break.
Consideration has also been given to equipping the flap with ties, each of which connects one of its edges to the dashboard body so as to restrict its movement in order to limit the extent to which it can open. However, the presence of lateral ties reduces the area through which the airbag is deployed, it then no longer being possible for the airbag to be deployed laterally in satisfactory manner. In addition, the forces involved during the deployment are such that those ties are torn off or else brake the deployment of the airbag if they are strong enough.
It must be possible for the airbag to be deployed effectively both in the frontal direction and also in the lateral directions so as to enable an occupant seated in a non-conventional position on the seat to be protected reliably.